From left, Abdulmajeed and his wife, Baraa, Syrian refugees, were greeted by her father at O’Hare International Airport in Chicago on Tuesday. They were allowed to enter the country after a federal judge blocked key parts of President Trump’s immigration ban.CreditCreditAlyssa Schukar for The New York Times

WASHINGTON — A federal appeals panel on Thursday unanimously rejected President Trump’s bid to reinstate his ban on travel into the United States from seven largely Muslim nations, a sweeping rebuke of the administration’s claim that the courts have no role as a check on the president.

The three-judge panel, suggesting that the ban did not advance national security, said the administration had shown “no evidence” that anyone from the seven nations — Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen — had committed terrorist acts in the United States.

The ruling also rejected Mr. Trump’s claim that courts are powerless to review a president’s national security assessments. Judges have a crucial role to play in a constitutional democracy, the court said.

Approved refugees and visa holders from the seven countries listed in President Trump’s immigration order were able to enter the country after judges suspended the move.Published OnFeb. 6, 2017CreditCreditAlex Wroblewski for The New York Times

The decision was handed down by the United States Court of Appeals for the Ninth Circuit, in San Francisco. It upheld a ruling last Friday by a federal district judge, James L. Robart, who blocked key parts of the travel ban, allowing thousands of foreigners to enter the country.

The appeals court acknowledged that Mr. Trump was owed deference on his immigration and national security policies. But it said he was claiming something more — that “national security concerns are unreviewable, even if those actions potentially contravene constitutional rights and protections.”

Within minutes of the ruling, Mr. Trump angrily vowed to fight it, presumably in an appeal to the Supreme Court.

“SEE YOU IN COURT, THE SECURITY OF OUR NATION IS AT STAKE!” Mr. Trump wrote on Twitter.

At the White House, the president told reporters that the ruling was “a political decision” and predicted that his administration would win an appeal “in my opinion, very easily.” He said he had not yet conferred with his attorney general, Jeff Sessions, on the matter.

The Supreme Court remains short-handed and could deadlock. A 4-to-4 tie there would leave the appeals court’s ruling in place. The administration has moved fast in the case so far, and it is likely to file an emergency application to the Supreme Court in a day or two. The court typically asks for a prompt response from the other side, and it could rule soon after it received one. A decision next week, either to reinstate the ban or to continue to block it, is possible.

The travel ban, one of the first executive orders Mr. Trump issued after taking office, suspended worldwide refugee entry into the United States. It also barred visitors from seven Muslim-majority nations for up to 90 days to give federal security agencies time to impose stricter vetting processes.

Immediately after it was issued, the ban spurred chaos at airports and protests nationwide as foreign travelers found themselves stranded at immigration checkpoints by a policy that critics derided as un-American. The State Department said up to 60,000 foreigners’ visas were canceled in the days immediately after the ban was imposed.

The World Relief Corporation, one of the agencies that resettles refugees in the United States, called the ruling “fabulous news” for 275 newcomers who are scheduled to arrive in the next week, many of whom will be reunited with family.

“We have families that have been separated for years by terror, war and persecution,” said Scott Arbeiter, the president of the organization, which will arrange for housing and jobs for the refugees in cities including Seattle; Spokane, Wash.; and Sacramento.

“Some family members had already been vetted and cleared and were standing with tickets, and were then told they couldn’t travel,” Mr. Arbeiter said. “So the hope of reunification was crushed, and now they will be admitted.”

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Bob Ferguson, the attorney general of Washington State, said the rebuke of Donald J. Trump’s travel ban by a federal appeals court panel was a "complete victory."Published OnFeb. 9, 2017CreditCreditAssociated Press

Several Democrats said they hoped the appeals court ruling would cow Mr. Trump into rescinding the ban. Representative Karen Bass, Democrat of California, said in a statement that the ban “is rooted in bigotry and, most importantly, it’s illegal.”

“We will not stop,” Ms. Bass said.

But some Republicans cast aspersions on the Ninth Circuit’s decision and predicted that it would not withstand a challenge in the Supreme Court.

“Courts ought not second-guess sensitive national security decisions of the president,” Senator Tom Cotton, Republican of Arkansas, said in a statement.

“This misguided ruling is from the Ninth Circuit, the most notoriously left-wing court in America, and the most-reversed court at the Supreme Court,” he said. “I’m confident the administration’s position will ultimately prevail.”

Trial judges nationwide have blocked aspects of Mr. Trump’s executive order, but no other case has yet reached an appeals court. The case in front of Judge Robart, in Seattle, was filed by the states of Washington and Minnesota and is still at an early stage. The appeals court order issued Thursday ruled only on the narrow question of whether to stay a lower court’s temporary restraining order blocking the travel ban.

The appeals court said the government had not justified suspending travel from the seven countries. “The government has pointed to no evidence,” the decision said, “that any alien from any of the countries named in the order has perpetrated a terrorist attack in the United States.”

The three members of the panel were Judge Michelle T. Friedland, appointed by President Barack Obama; Judge William C. Canby Jr., appointed by President Jimmy Carter; and Judge Richard R. Clifton, appointed by President George W. Bush.

They said the states were likely to succeed at the end of the day because Mr. Trump’s order appeared to violate the due process rights of lawful permanent residents, people holding visas and refugees.

The court said the administration’s legal position in the case had been a moving target. It noted that Donald F. McGahn II, the White House counsel, had issued “authoritative guidance” several days after the executive order came out, saying it did not apply to lawful permanent residents. But the court said that “we cannot rely” on that statement.

“The White House counsel is not the president,” the decision said, “and he is not known to be in the chain of command for any of the executive departments.“ It also mentioned “the government’s shifting interpretations” of the executive order.

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The activist Michael Petrelis outside of the Ninth United States Circuit Court of Appeals in San Francisco on Thursday after the ruling was announced.CreditJim Wilson/The New York Times

In its briefs and in the arguments before the panel on Tuesday, the Justice Department’s position evolved. As the case progressed, the administration offered a backup plea for at least a partial victory.

At most, a Justice Department brief said, “previously admitted aliens who are temporarily abroad now or who wish to travel and return to the United States in the future” should be allowed to enter the country despite the ban.

The appeals court ultimately rejected that request, however, saying that people in the United States without authorization have due process rights, as do citizens with relatives who wish to travel to the United States.

The court discussed, but did not decide, whether the executive order violated the First Amendment’s ban on government establishment of religion by disfavoring Muslims.

It noted that the states challenging the executive order “have offered evidence of numerous statements by the president about his intent to implement a ‘Muslim ban.’” And it said, rejecting another administration argument, that it was free to consider evidence about the motivation behind laws that draw seemingly neutral distinctions.

But the court said it would defer a decision on the question of religious discrimination.

“The political branches are far better equipped to make appropriate distinctions,” the decision said. “For now, it is enough for us to conclude that the government has failed to establish that it will likely succeed on its due process argument in this appeal.”

The court also acknowledged “the massive attention this case has garnered at even the most preliminary stages.”

“On the one hand, the public has a powerful interest in national security and in the ability of an elected president to enact policies,” the decision said. “And on the other, the public also has an interest in free flow of travel, in avoiding separation of families, and in freedom from discrimination.”

“These competing public interests,” the court said, “do not justify a stay.”

The court ruling did not affect one part of the executive order: the cap of 50,000 refugees to be admitted in the 2017 fiscal year. That is down from the 110,000 ceiling put in place under President Barack Obama. The order also directed the secretary of state and the secretary of homeland security to prioritize refugee claims made by persecuted members of religious minorities.

As of Thursday, that means the United States will be allowed to accept only about 16,000 more refugees this fiscal year. Since Oct. 1, the start of the fiscal year, 33,929 refugees have been admitted, 5,179 of them Syrians.